You have to understand that the CORS behavior is not an error — it’s a mechanism that’s working as expected in order to protect your users, you, or the site you’re calling. If I understood it right you are doing an XMLHttpRequest to a different domain than your page is on. So the browser is blocking it as it usually allows a request in the same origin for security reasons. You need to do something different when you want to do a cross-domain request. In this case you need to enable your service for CORS which is cross origin resource sharing.
If you want to bypass that restriction when fetching the contents with fetch API or XMLHttpRequest in javascript, you can use a proxy server so that it sets the header Access-Control-Allow-Origin to *.
If you need to enable CORS on the server in case of localhost, you need to have the following on request header.
Access-Control-Allow-Origin: http://localhost:9999